atypical thyroid symptoms

Some patients with fatigue have had thyroid testing which proved to be normal. The fatigue may, however, be caused by reverse T3 (rT3) thyroid syndrome which is different from simple hypothyroidism, or under functioning of the thyroid. The presence of high amounts of rT3 will suppress cell thyroid signal even in the presence of normal amounts of thyroid hormone. The TSH which is used to determine thyroid hormone function will often be normal in the presence of rT3 syndrome as the production of TSH only indicates the presence of adequate normal thyroid hormone. The fatigue is caused by the lack of effect of the thyroid hormone at the cell level because too many of the cell thyroid hormone receptors are being taken up by the inactive rT3 present.

The cause of high rT3 production is the presence of high cortisol. Both the thyroid hormones and adrenal hormones (cortisol) activate cell energy production. If both thyroid hormone and cortisol were very active at the same time, it would be too stimulating. This is prevented when cortisol is too high by its inactivation of thyroid hormone by the conversion of much of it to rT3.

Because both cortisol and thyroid hormones activate cell energy, cells are carefully regulated to protect cells from too much activation from intense cortisol and thyroid hormone activation at the same time. The thyroid gland makes hormone predominantly as T4. As shown above this is a molecule with an iodine on each of four corners hence the name T4. This circulating form has lower cell activating properties, and most T4 once it enters a cell will have an iodine removed from one corner by an enzyme called a deiodinase making it a more active hormone, T3. The T3 fits into a receptor triggering cell activation.

When cortisol levels are high, cells protect themselves from overstimulating by both cortisol and thyroid hormone. The high cortisol causes the cell to produce another enzyme called a reverse deiodinase, or type II deiodinase.

The type II deiodinase enzyme knocks an iodine off the wrong corner making an inactive molecule rT3. Reverse T3 will fit into the hormone receptors but will not trigger cell activation. It also prevents active T3 from doing so, hence the “hypothyroid effect”.

Standard testing for thyroid related fatigue typically only looks at “how much” and not “why”. How much testing is done simply to judge the need for thyroid hormone replacement therapy. Some thyroid dysfunction results from autoimmune attack on the thyroid triggered by things such as food sensitivities. The answer in this case is often isolating the cause and removing it allowing the thyroid to normalize its own function. Many patients have had limited thyroid testing and been told that is not the problem when it may be. Comprehensive testing should involve looking at the pituitary signal to the thyroid (TSH), thyroid antibodies, as well as free thyroid hormones.